Reservoir for writing or dispensing instruments



Oc 8, 96 H. R. FEHLING EIAL 3,106,190

RESERVOIR FOR WRITING OR DISPENSING INSTRUMENTS Filed July 20, 1961 2Sheets -Sheet 1 INVENTORS HANS REINHARD FEHLING 8| EDWARD HENRY HARVEYheir ATTORNEYS 1963 H; R. FEHLING ETAL 3,106,190

' RESERVOIR F'OR WRITING 0R DISPENSING INSTRUMENTS Filed July 20, 1961 2Sheets -Shee t, 2

INVENTORS HANS REINHARD FEHLING 8 EDWARD HENRY HARVEY their ATTORNEYSUnited States Patent 3,106,190 RESERVOIR FOR WRITlN G OR DISPENSINGINSTRUMENTS Hans Reinhard Fehling, Zug, Switzerland, and Edward HenryHarvey, London, England, assignors to I.R.C. Limited, London, England, acompany of Great Britain Filed July 20, 1961, Ser. No. 125,551 Claimspriority, application Great Britain July 30, 1960 12 C. (Cl. 120-424)This invention relates to liquid reservoirs for writing or otherdispensing instruments and, more particularly, to a new and improvedliquid reservoir for liquids of relatively low viscosity.

This application is a continuation-impart of our copending applicationfor Seal for Reservoirs of Writing and Other Dispensing Instruments,Serial No. 5,872, filed February 1, 1960. In our copending applicationthere is described a seal for a liquid reservoir having a bore open atone end to the exterior of the reservoir and a dispensing device such asa writing tip communicating with the other end of the bore comprising apiston follower slidable in the bore and forming a clearance space ofcapillary dimensions therewith, along with means for urging the followerin the direction out of a liquid contained in the reservoir so as tooppose the capillary force of a liquid meniscus in the clearance spacesurrounding the follower which tends to draw the follower into thereservoir liquid. In one of the embodiments described in the copendingapplication the urging means is acompression spring located within thereservoir while in another embodiment the urging means is a tensionspring extending from the follower to the reservoir at a point near theopen end of the bore.

In all of the embodiments described in the copending application and inmost conventional ball-point writing instruments the weight of theliquid column when the reservoir is in the upright position produces aliquid pressure or head at the writing tip which tends to force liquidout of the tip. With relatively viscous and quick drying inks of thetype now used in ball-point pens, which have a viscosity of about onehundred poise at 25 C., practically no ink flows through the tip beforethe ink at the tip dries to form a seal. If a non-drying or slow dryingink or a less viscous ink is used in a conventional reservoir, however,objectionable leakage of ink through the writing tip can occur when thereservoir is in the upright position because of the pressure produced atthe tip by the weight of the liquid column.

Accordingly, it is an object of this invention to provide a new andimproved liquid reservoir for dispensing instruments which overcomes theabove-mentioned shortcomings of conventional reservoirs.

Another object of the present invention is to provide an improvedreservoir for dispensing instruments especially adapted to hold liquidsof relatively low viscosity.

A further object of the invention is to provide a reservoir of the abovetype wherein the liquid pressure at the dispensing end remainssubstantially constant as liquid is withdrawn from the reservoir.

These and other objects of the invention are accomplished by providing areservoir with a supply conduit having a bore which is open at one endto the exterior of the reservoir and a discharge duct which leads fromthe other end of the bore to a dispensing extremity located farther fromsaid other end of the bore than is the open end in a direction oppositeto the direction from the open end to the other end of the bore. Inaddition, the reservoir is provided with a piston which is slidable inthe bore and forms a clearance space of capillary dimensions therewithand .with means for urging the piston toward the open end of the borewith increasing force as the piston moves away from the open end butwith insufficient force to drive the piston out of a liquid contained inthe bore. In one embodiment of the invention the urging means comprisesa compression spring located within the bore and the change in springforce per unit change in length of the spring is approxi materialy equalto the change in the liquid pressure or head at the dispensing extremityresulting from withdrawal of liquid from the reservoir.

Further objects and advantages of the invention will be apparent from areading of the following description in conjunction with theaccompanying drawings, in which:

FIGURE 1 is a view in longitudinal section through a typical writinginstrument having a reservoir arranged accordingto the presentinvention;

FIGURE 2 is a view in longitudinal section through a complete handwriting instrument incorporating a reservoir according to thisinvention;

IFIGURES 3 and 4 are cross-sectional views taken respectively on thelines lII-III and IVIV in FIG- URE 2;

FIGURES 5, 6 and 7, respectively, are views in longitudinal sectionthrough three further instrument units according .to this invention; andi FIGURE 8 is a fragmentary view showing another type of reservoirfollower according to the invention.

While the present invention is applicable to reservoirs of writinginstruments such as fountain pens, stylographic pens, and ball-pens andball-point pens, it is also applicable to dispensing instruments orapplicators (primarily those having a ball-tip or ball-valve dischargeend) such ,as may be used for dispensing or applying deodorants,

scent and other, cosmetics. It is especially applicable to thereservoirs of ball-point writing instruments, for the difiiculties whichthe invention seeks to reduce have chiefly arisen in connection withball-point writing instruments. Accordingly, the invention is describedherein with reference to ball-point writing instruments.

Turning now to FIGURE 1 the reservoir 10 (constituting a supply ducthaving a bore open at one end to the exterior of the reservoir) containsa column 11 of ink or other liquid to be dispensed and at the head ofthis column there is a slidable piston or follower 12 which is urgedtoward the open, or vented, end 13 of the reservoir by a compressionspring 14 contained within the reservoir. The liquid 11 fills the narrowannular gap or clearance between the periphery of the follower 12 andthe interior of the reservoir 10 and the spring 14 exerts on thefollower 12, in all attitudes of the reservoir, a force which is sodirected that it tends to urge the follower out of the reservoir liquidin which it is wholly or partly immersed andbeing large enough tobalance in any attitude of the reservoir all other forces which tend tourge the follower further into the liquid. If desired, a sealing liquiddifferent from the reservoir liquid may be provided in the clearanceabout the follower 12.

In a conventional reservoir utilizing a piston follower to form theseal, one end or face of the follower is immersed in the liquid whilstthe other end or face (which is subject to atmospheric pressure) emergesfrom it with the result that at the latter end a small meniscus isformed at the surface of the thin annulus of liquid filling theclearance between the follower periphery and the reservoir Wall.

If this meniscus is concave, the resulting capillary forces produce adepression (below atmospheric pressure) in this annulus of liquid. Inconsequence there is a pressure difference between the two faces or endsof the follower which, even if the latter has the same bulk density(apparent specific gravity) as the liquid, tends to force the followerinto the liquid.

If this force is not balanced by an opposing force, the follower willmove into the liquid and extrude the latter through the above-mentionedannular clearance. This condition occurs when the reservoir lies on itsside. Movement of the follower into the liquid will continue until theconcave meniscus changes its shape in such a way that the resultingcapillary forces no longer reduce the hydrostatic pressure in thereservoir, i.e., when in effect the pressure difference between the twoends of the follower has vanished. The capillary pressure can onlydecrease if the radius of the meniscus increases, i.e., if a strong,stable meniscus changes into a weak and usually unstable meniscus,whether slightly convex or slightly concave. When this happens there isdanger of liquid seepage toward the rear end of the reservoir,especially if there already exists a film of liquid on the reservoirwall behind the follower (as may happen due to the liquid level beinglowered by the dispensing of liquid).

There is another and additional reason'why there is danger of seepage.When the reservoir is lying on its side, the annulus of liquid betweenthe follower periphery and the reservoir wall, at the lower part of thefollower periphery, is subjected to a positive hydrostatic head themagnitude of which is proportional to the diameter (or equivalentdimension) of the reservoir. Hence it is at this lower part of thefollower periphery that liquid seepage takes place, unless thehydrostatic head at each point of the annular surface of the liquid isbalanced by the local capillary pressure (depending on the local radiusof curvature of the liquid surface).

In this specification the expression strong meniscus is used to indicatea meniscus which is very stable (and not one where the surface tensionforce is particularly high, for surface tension is constant andindependent of curvature) the most important feature producing stabilityis a small radius of curvature, because such a meniscus will notpractically change its shape in various positions of the instrument.

Accordingly, as described in the above-mentioned copending application,the spring 14 balances the capillary pressure by urging the follower 12out of the reservoir liquid with a force which is sufficiently high toprevent seepage of liquid past the follower but is not higher than theforces on the follower resulting from the formation of a liquid meniscusin the annular clearance.

In a liquid reservoir of the type described herein it may also bedesirable, or even essential, that the head under which the liquid isdispensed (or fed to the writing extremity) varies but little, or evenremains substantially constant, while the reservoir empties. In a normalfountain pen the problem of maintaining substantially constant liquidpressure at the writing point is solved by allowing the air whichreplaces the ink to move up into a closed reservoir through the samechannel as that through which the ink flows down. The result is that thehead of liquid in the reservoir is approximately balanced by the airpressure in the reservoir which is, or should be, slightly belowatmospheric. However, it is well known that this system is sensitive tochanges in temperature and pressures of the surrounding atmosphere andthat a normal fountain pen is particularly liable to leakage in modernair travel unless certain precautions are taken. As will be appreciatedfrom the ensuing description a reservoir according to the presentinvention is less prone to leakage due to temperature and pressurevariations.

In accordance with the present invention, therefore, the liquidreservoir is provided with means for exerting on the follower, at leastin the operative attitude of the reservoir, a force which opposesmovement of the follower along the bore as the liquid is discharged andincreases with the distance travelled by the follower but isinsufficient to eject the follower from the liquid, and with a dischargeconduit leading from the rear end of the bore in a direction opposite tothe said travel of the I a follower. The expression opposite is used ina broad sense to indicate that if the-bore is upright, or extendsupwards, the discharge conduit extends in a downwards direction, forwhich purpose the discharge conduit may be parallel to, or at an angleto, the bore.

In the embodiment shown in FIGURE 1, there is a discharge conduit 15leading from the inner end of the reservoir bore (toward which thefollower =12 moves as liquid is dispensed) in a direction opposite thetravel of the follower. The conduit 15, which is preferably of smalldiameter, terminates in a ballpoint writing extremity 16 located beyondthe open end 13 of the bore. It will be appreciated that since themovement of the follower along the bore is opposed by the force of thespring 14-, which increases with the distance travelled by the follower12, and the discharge conduit leads in a direction opposite to thefollower travel, the capillary pressure set up by said force tends tonullify the variation in head that would otherwise occur at the writingextremity 1-6 as the length of the liquid column 11 in the boredecreases upon discharge through said conduit. Indeed if the rate ofchange of the capillary pressure set up by said force (per unit lengthof the bore) is equal to the rate of change of the liquid head, the twocancel one another and delivery under a constant or substantiallyconstant head is achieved. To accomplish this the spring rate orstiffness is made equal to the rate of change of liquid head in thereservoir. The spring rate is the change in spring force per unit changein length of the spring: the rate of change of liquid head is the changein hydrostatic thrust on the foilower per unit change in the length ofthe liquid column.

Considering the writing instrument in the typical writing attitude shownin FIGURE 1 in which the reservoir 10 extends upwards, and the dischargeconduit 15 downwards, at angle H, it can be shown that, if the springrate is equal to the rate of change of liquid head, then throughout thelife of the reservoir (i.e., irrespective of the volume of ink remainingin the reservoir) the head of ink at the writing extremity is constantand, in partitcular, that, at a given point in the discharge conduit 15,indicated at C in FIGURE 1, the pressure is equal to the atmosphericpressure.

In our aforesaid copending application it has been shown that the springexercises an outward thrust on the follower which is balanced by thecapillary forces of the meniscus set up between the follower and thereservoir walls. This capillary pressure is, in effect, equivalent to anegative head of liquid which increases as the reservoir empties,because the spring becomes more compressed and the outward throustincreases correspondingly.

In the attitude shown in FIGURE 1 the positive head of liquid in thedischarge conduit 15 is partly balanced by the negative head of liquidin the reservoir 1% itself. This negative head is assisted by thecapillary pressure produced by the outward thrust of spring 14. As thereservoir 10 empties the negative head due to the liquid column in thereservoir diminishes, whereas the negative head due to the capillarypressure increases because of the increased outward thrust of thespring. If the spring is suitably designed, these variations will justcancel one another so that the total negative head opposing the constantpositive head in the discharge conduit 15 remains constant. For thispurpose the spring rate is made equal to the rate of change of liquidhead in the following manner:

S=AW sin H (1) in which S is the spring rate (gm/cm.) A thecross-sectional area of the piston (cm?) W the specific gravity of theliquid H the angle of the reservoir in the normal position of use.

In order to achieve the correct spring rate according to this condition,the wire diameter of the spring has to be chosen according to thefollowing formula:

in which a is the diameter of the wire (cm.)

B is the diameter of the spring (cm.)

n the number of turns of the spring G the rigidity modulus of the wirematerial (gm./cm.

The directions for determining the minimum and maximum outward thrustwhich the spring 14 should exert on the follower 12 in order to preventleakage, as well as to prevent any instability of the annular meniscus,are set out in detail in the above-mentioned copending application.These directions, together with the spring rate as determined accordingto Formula 1, govern the usable length L of the ink column shown inFIGURE 1.

In order to determine the design factors controlling the head underwhich the liquid is to be dispensed, it is best first to determine atwhich point along the length of the discharge conduit 15 the head shouldbe zero under the combined influence of the head of liquid in thereservoir and the negative head produced by the outward thrust of thespring 14 on the follower 12. In the particular embodiment shown inFIGURE 1, the position of this balance point is indicated at C. Thedesired balance is achieved if the length of the liquid column in thedischarge conduit 15 down to the point C is equal to the freeuncompressed length L of the spring 14 plus the length L of follower 12(assuming the overall specific gravity or bulk density of the latter isequal to that of the liquid 11) e If the spring is then compressed by anamount required to establish a stable meniscus by the minimum outwardthrust on the follower, the balance point C remains Where it wasprovided the spring rate is designed according to Formula 1. Hence ifthe writing extremity 16 were arranged to be at the balance point C, thehead would remain zero while the reservoir empties. On the other hand,if a slight constant head is required, this can be easily achieved byadjusting the total length of the discharge conduit accordingly toprovide an arrangement such as that shown in FIGURE 1. This is, ofcourse, only strictly true for one attitude of reservoir 10 anddischarge conduit 15, for the head will in fact vary slightly accordingto the angle H at which the instrument is held, but the variations aresmall and usually negligible. It will usually be best to design theinstrument in such a way that the maximum permissible or desirable headis obtained in the upright position so that any more inclined positionwill automatically result in lowering the total head.

It will be noted that in an instrument according to the invention, thereis no necessity to allow the ingress of air into the reservoir in orderto achieve the balance desired. Hence, such an instrument is entirelyinsensitive to external changes in temperature and pressure. This is, of

course, highly desirable in any writing instrument, but

particularly in those using rather fluid inks.

The following data are given by way of example, for a typical ball-pointpen according to the invention, assumming a normal use at an angle of 45degrees:

Mean radial clearance mm 0.05

6 Length of ink column in full reservoir, L cm 5 Length of feedcapillary to balance point, L-t-L About cm" 7.5 Total length ofinstrument, L cm 10 Head of liquid at the ball point (at 45 inclination)About cm 2 It will be appreciated that the reservoir unit shown inFIGURE 1 may be fitted to the barrel, case, or housing, of a handwritting instrument, and one manner of incorporating an equivalent unitin such a case or housing is illustrated FIGURES 2-4. It may here bementioned that the units shown respectively in FIGURES 2-4, FIG- URE 5,FIGURE 6, and FIGURE 7, are basically similar to that shown in FIGURE 1.Therefore, in each of these five units like parts have like referencenumbers with the addition of the index letter a in FIGURES 2-4, b inFIGURE 5, c in FIGURE 6, and d in FIGURE 7.

Turning now to FIGURES 2-4, the unit 17 shown therein has a reservoir10a, ink column 11a, piston or follower 12a, spring 14a, dischargeconduit 15a, and writing extremity 16a. It will be seen that the unit 17is so applied to the shaft or casing 18 of the instrument that thereservoir 10a lies in the interior of the casing but that the dischargeconduit 15a (with its reduced forward extremity 15a terminating in thewriting extremity 16a containing the writing ball 19) lies in alongitudinal groove in the exterior of the shaft 18. A vent for thereservoir is shown at 21. In accordance with the copending applicationof Fehling and Street, Serial No. 87,821, filed February 8, 1961, andassigned to the same assignee as the present application, the part 15'ais so ben-t that (a) the ball 19 is disposed at or near the longitudinalaxis 20 of the instrument 20 and preferably has a slight trail, and (b)the end portion of part 15a and at least the adjacent part of its bendare exposed at the surface of the shaft or casing 18 to the view of theuser in the act of writing. For full directions on these mattersreference is to be made to the above-identified application of Fehlingand Street.

Suitable dimensions in one example according to FIG- URE 2 are asfollows:

Reservoir bore (D) mm 6 Length of uncompressed spring (L) mm 61 Meandiameter of turns mm 4.75 Number of turns (n) 41 Wire diameter for brass(a) mm 0.11 Spring stiffness (S) gm./cm 0.19 Specific gravity of ink 1.1Length of piston (L mm 8 Mean radial clearance mm 0.05 Length of inkcolumn in full reservoir (L cm 3.5 Length of feed capillary to balancepoint (L+L,,)

About cm 7.5 Total length of instrument (L cm 9.7 Head of liquid at theball-point (at 45 inclination) About cm- 1.6

In the modified unit 22 shown in FIGURE 5, the discharge conduit 15bextends, concentrically with the bore of the reservoir 10b, along theaxis 10' of the latter. The follower 12b is therefore of annular form soas to slide along the annular cavity between the exterior of the conduit15b and the bore of the reservoir 10b, the necessary clearance betweenthe interior periphery of the follower 12b and the exterior peripheryofconduit 15b and between the exterior periphery of the follower and thebore of the reservoir being provided. Each clearance annulus is occupiedby sealing liquid (being, conveniently, the reservoir liquid) whichpresents a meniscus towards the air space at the lower end of thefollower, which space is vented at 21b.

Suitable dimensions in one example are as follows:

Reservoir bore (D) mm 5 Piston outside diameter mm 4.9

Piston inside diameter Q. mm 2.1 Discharge conduit outside diameter mm2.0 Discharge conduit internal diameter mm 1.5 Mean radial clearance mm0.05 Cross-sectional area of piston cm. 0.154 Length of piston mm 6Length of uncompressed spring (L) mm 61.5 Mean diameter of turns mm 4.75No. of turns (it) 65 Wire diameter for brass (a) mm 0.11 Springstiifness (S) grn./cm 0.12 Specific gravity of ink 1.1 Length of inkcolumn in full reservoir (L mm 43 Length of feed capillary to balancepoint (L+L About mm 68 Total length of instrument (L cm 9.65

Head of liquid at the ball-point (at 45 inclination) About cm 1.4

In the unit 23 shown in FIGURE 6 a metal ball 24 is interposed betweenthe follower 12c and the compression spring 140. In the normal writingattitude of the instrument, as shown, the ball 24 counteracts part ofthe positive head at the ball point (i.e., the point of balanceindicated at C in FIGURE 1 is effectively lowered). However, when theunit 23 is inverted so that the nib 160 is uppermost, the ball 24 eitherpartially or wholly compresses the spring 140 with the result that thenegative head at the point C is reduced to a fraction of the value whichwould prevail were the ball not present. This reduces any tendency forthe to run back from the ball point when the unit is in the invertedposition.

In the construction shown in FIGURE 6 the follower 12c should be madeslightly buoyant in the ink in order that it shall not sink into the inkwhen the ball 24 compresses spring 140.

The unit 25 shown in FIGURE 7 resembles in all material respects theunits shown in FIGURES 1 to 4 except in that a secondary follower l2d isslidably disposed in the bore of the reservoir d beyond the follower12d. The annular clearance between this secondary follower 12d and thebore of the reservoir is sealed with a sealing liquid having a viscosityof the order of 100 poise, so that, if the secondary follower 12'd isindependent of the follower 12d, air or other gas is trapped in thespace 26 between the two followers.

The follower -12d is shown as being of cylindrical form and it mayincorporate a reservoir 27 for the sealing liquid comprising capillaryslots or holes in the outer end of the follower substantially asdescribed in our copending application for Reservoir Seal for Writing Instrument, Serial No. 125,552, filed July 1961.

The secondary follower 12d acts as a viscous damper upon the liquid inthe reservoir by virtue of the resistance to shear exhibited by its highviscosity sealing liquid combined with the resistance of the trapped airto change in volume. For this purpose the trapped air volume should bekept to a minimum by having a small gap of, say, 2 mm. between the twofollowers. This viscous damping effect is of importance if the reservoirliquid itself is of low viscosity, as for example in a fountain pen,since it prevents break up of the reservoir column when the unit issubjected to shock.

If the secondary follower 12d is made of high density material, e.g.,copper or steel, it also operates substantially in the manner of ball 24in FIGURE 6, for the gas or air trapped in space 26 functions like aspring connecting the two followers so that the elfect of the weight offollower 1221' is transmitted by this air spring to follower 12d. Whenthe unit is held in the normal writing attitude, the heavy secondaryfollower 12'd tends to move downwards (causing a reduction in pressureof the trapped gas) but is elastically suspended from follower -12d bythe trapped gas so that it operates to eifect a reduction of thepositive head at the ball point in substantially the same manner as theball 24. When the unit is inverted, the secondary follower lZ'd tends toslide down toward follower 12d, and therefore compresses the trappedgas. Its weight eifect is therefore transmitted by the trapped gas tofollower 12d thereby wholly or partially counteracting the effect ofspring 14d.

The capillary pressure diiferential across the ink meniscus remainsunaltered despite variations of the pressure of the trapped air withvarying angles of inclination. The pressure of the trapped air must ofcourse remain within the limits laid down for such a liquid-sealed airspace in our copending application, Serial No. 5,872.

In an alternative arrangement, illustrated in FIGURE 8, the secondaryfollower 12c is connected to the follower 12a which is in contact withthe reservoir liquid, and the air space 26 is preferably vented toatmosphere via a hole 28 in the secondary follower. In this arrangementthe shock-damping effect of the viscous sealing liquid around thesecondary follower 12c is transmitted, by means of the connection, tothe follower 122 which is in contact with the reservoir liquid. Underconditions of shock, the latter then behaves as if it were rigidlyattached to the reservoir wall, and there is no danger of disturbing'thelow viscosity reservoir liquid.

In all the instruments described herein the force exerted on thefollower must normally, in all attitudes of the instrument, beinsufficient to overcome completely the capillary forces in the narrowgap between the writing ball and its housing. If, however, after thefollower has reached the upper limits of its travel, writing iscontinued, the positive head then prevailing may be adequate to overcomethe capillary forces in the clearance around the follower so that theink is withdrawn from that clearance, or the liquid seal around thefollower is broken, and since air is then able to pass the follower, thelatter is forced down by the spring. In certain cases it may then bepossible to continue writing until the discharge duct 15 is empty, butthe balanced condition described herein will, obviously, no longerexist.

Although the invention has been described herein with reference tospecific embodiments, many modifications and variations therein willreadily occur to those skilled in the art. Accordingly, all suchvariations and modifications are included within the intended scope ofthe invention as defined by the following claims.

We claim:

1. A liquid reservoir comprising a supply conduit having a bore open atone end to the exterior of the reservoir, a discharge duct leading fromthe other end of the bore to a dispensing extremity which is locatedfarther from said other end of the bore than is the open end of the borein a direction opposite to the direction from the open end of the boreto the other end of the bore, a piston slidable within the bore of theconduit having a crosssectional shape similar to but slightly smallerthan that of the conduit bore to provide a clearance of capillarydimensions between the adjacent surfaces of the piston and the conduit,and means for urging the piston toward the open end of the conduit withincreasing force as the piston moves away from the open end but withinsuflicient force to drive the piston out of a liquid contained in thebore, thereby tending to compensate for the increase in liquid pressureat the dispensing extremity resulting from withdrawal of liquid from thereservoir when said extremity is below the piston in the conduit bore.

2. A liquid reservoir according to claim 1 wherein the discharge ductextends parallel to the conduit bore.

3. A liquid reservoir according to claim 1 wherein the means for urgingthe piston toward the open end of the conduit comprises a springextending between the piston and a fixed point on the conduit.

4. A liquid reservoir according to claim 3 wherein the spring is acompression spring extending from the piston to the end of the conduitat which the conduit bore communicates with the discharge duct.

5. A liquid reservoir according to claim 3 wherein the change in springorce per unit change in length of the spring is approximately equal tothe change in force applied to the piston by a column of liquid in theconduit bore per unit change in length of the column.

6, A liquid reservoir according to claim 1 wherein the force applied bythe urging means is suiiicient to produce a balance point in thedischarge duct which is between the dispensing extremity and a pointspaced from the junction of the discharge duct with the supply conduitby a distance equal to the length of the supply conduit.

7. A liquid reservoir according to claim 1 wherein the discharge ductextends axially through the bore and the piston has a central aperturethrough which the discharge duct passes.

8. A liquid reservoir according to claim 3 including a weight interposedbetween the spring and the piston.

9. A liquid reservoir according to claim 1 including a secondaryfollower slidable within the bore located between the first-mentionedpiston and the open end of the bore, and a body of liquid surroundingthe secondary follower and forming a seal between it and the conduit,thereby providing, in conjunction with the first-mentioned piston, aclosed space to contain a trapped body of gas.

10. In combination, a liquid reservoir according to claim '1 wherein thedischarge duct extends parallel to and along one side of the supplyconduit and a holder comprising a shaft having an elongated centralcavity to receive the supply conduit and having a longitudinal slot inits outer surface to receive the discharge duct.

11. A liquid reservoir comprising a supply conduit having a bore whichis subject to atmospheric pressure at one end, a discharge duct leadingfrom the other end of the bore to a dispensing extremity which islocated farther from said other end of the bore than is said one end ofthe bore in a direction opposite to the direction from said one end or"the bore to the other end of the bore, a piston slidable within the boreof the conduit having a cross-sectional shape similar to but slightlysmaller than that of the conduit bore to provide a clearance ofcapillary one end of the conduit with increasing force as the pistonmoves away from the said one end but with insufiicient force to drivethe piston out of a liquid contained in the bore, thereby tending tocompensate for the increase in liquid pressure at the dispensingextremity resulting from withdrawal of liquid from the reservoir whensaid extrernity is below the piston in the conduit bore.

12. A liquid reservoir comprising a supply conduit formed with a borewhich is subject to atmospheric pressure at one end and forms a junctionwith a discharge duct at the other end, a discharge d-uct leading fromthe junction to a dispensing extremity, the distance between thedispensing extremity and the junction being greater than the distancebetween said one end and the junction and also greater than the distancebetween said one end and the dispensing extremity, a piston slidablewithin the bore of the conduit having a cross-sectional shape similar tobut slightly smaller than that of the conduit bore to provide aclearance of capillary dimensions between the adjacent surfaces of thepiston and the conduit bore, said piston being adapted to move at theend of a column of liquid in the bore in a direction from said one endtoward the junction with the discharge duct, and means for urging thepiston toward said one end of the conduit as the piston moves away fromsaid one end but with insufficient force to drive the piston out of aliquid contained in the bore, thereby tending to compensate for theincrease in liquid pressure at the dispensing extremity resulting fromwithdrawal of liquid from the reservoir when said extremity is at alower level than the piston in the conduit bore.

References {Iited in the file of this patent UNITED STATES PATENTS2,672,137 Fehling Mar. 16, 1954 FOREIGN PATENTS 158,350 Australia Aug.19, 1954 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatentNo. 3 106. 190 October 8 1963 Hans Reinhard Fehling et all he abovenumbered pat- It is hereby certified that error appears in 0 Patentshould read as ent requiring correction and that the said Letterscorrected below.

Column 2, lines 6 and 7, for approximaterialy" read approximately column4, line 51, for "throust" read thrust, column 10, line 37. for "2,672137" read Signed and sealed this 7th day of April 1964.

SEAL) A Eowmm l BRENNER ERNEST W, SWIDER Attesting Officer Commissionerof Patents

12. A LIQUID RESERVOIR COMPRISING A SUPPLY CONDUIT FORMED WITH A BOREWHICH IS SUBJECT TO ATMOSPHERIC PRESSURE AT ONE END AND FORMS A JUNCTIONWITH A DISCHARGE DUCT AT THE OTHER END, A DISCHARGE DUCT LEADING FROMTHE JUNCTION TO A DISPENSING EXTREMITY, THE DISTANCE BETWEEN THEDISPENSING EXTREMITY AND THE JUNCTION BEING GREATER THAN THE DISTANCEBETWEEN SAID ONE END AND THE JUNCTION AND ALSO GREATER THAN THE DISTANCEBETWEEN SAID ONE END AND THE DISPENSING EXTREMITY, A PISTON SLIDABLEWITHIN THE BORE OF THE CONDUIT HAVING A CROSS-SECTIONAL SHAPE SIMILAR TOBUT SLIGHTLY SMALLER THAN THAT OF THE CONDUIT BORE TO PROVIDE ACLEARANCE OF CAPILLARY DIMENSIONS BETWEEN THE ADJACENT SURFACES